SPOILERS
It's difficult to change you alignment in BG2, but it is possible in places. The most obvious of which is the "Hell Tests." Chances are you took some of the evil paths there, and it shifted your alignment at some point.
You can cheat to change it back, if you use "
Shadow Keeper." I doubt there's any legimitate way to fix it.
There is a mod "Virtue" that complexifies the alignment system, making it easier to gain or lose alignment (i.e. ala Torment or NWN:SOU). Doesn't sound like this is your cup of tea, though.
As far as permenent party member death goes,this is something that has always been possible in BG or BG2. It simply means that prior to dying your party member took an incredibly large amount of damage. The only way to fix this is to reload.